Thanks for your somments, guys. The ripples are 2 imagemaps, and I'm still trying to do something procedurally. I agree about the roughish part in the center. I am also not satisfied with the whitish color. It could be watered/smudged bird droppings, but it's not recognizable as 'something'. The only floating foam is in the water. The 'clams' are just fake stones with a hard color variation, but I like the effect too. The wet areas are also a bit bumpy (watered down sand ridges), and for real water remnants they have to go.
The stream is just a simple shape, but something like this will have to be built from a wider area with actual creeks.
For wettish mud I usually use non-RT reflection with a reflectiveness of something like 0.2-0.5 and roughness 0.2, highlight intensity also down to 0.5, but it depends on how wet your mud needs to be. For the watery bits, full reflectivity and roughness 0.01 or so. I didn't use RT, but added some localized (Simple shapes) RT reflective areas where it's really beneficial (for a reflected plant or bird or so). All to keep render times low